Geological Structures
Dr. Ahmad Redaa
2025-02-11
Definition of Geological Structures
- Geological structures refer to the arrangement and
deformation of rocks in the Earth’s crust due to tectonic
forces, stress, and strain.
- They provide evidence of past geological events
such as mountain formation, earthquakes, and plate movements.
- Significance:
- Helps in geological mapping and resource
exploration.
- Provides insights into earthquake risks and tectonic
activity.
Forces Acting on Rocks
Stress vs. Strain
- Stress → The force applied to a
rock.
- Strain → The deformation caused by
stress.
Types of Tectonic Forces:
- Tension → Stretches rocks apart.
- Compression → Pushes rocks together.
- Torsion → Twisting forces.
- Shear → Sideways motion.
Classification of Geological structures
- Primary Structures → Formed during rock
deposition.
- Secondary Structures → Formed due to later
deformation.
- Unconformities → Gaps in geological records.
Primary Structures
- Definition:
- Structures formed during sediment deposition or rock
formation.
- Examples:
- Stratification (Bedding)
- Graded Bedding
- Cross Bedding
- Ripple Marks
- Mud Cracks
- These were discussed in the previous lecture on sedimentary
structures.
Secondary Structures
- Definition:
- Structures formed due to tectonic forces, stress, and
deformation.
- Includes:
- Folds
- Faults
- Joints
Folds
Definition:
- Bending of rock layers due to compression
forces.
Fold Geometry:
- Axial Plane → Divides the fold into two limbs.
- Crest → Highest point of a fold.
- Trough → Lowest point of a fold.
- Limb → Sides of the fold.
Types of Folds
Based on Symmetry:
- Symmetrical Folds → Limbs are equally
inclined.
- Asymmetrical Folds → Limbs dip at different
angles.
Based on Limb Inclination:
